1. Field of the Invention
The present invention relates to a method for testing oscillation characteristics of quartz oscillators, ceramic oscillators, or the like.
2. Description of the Related Art
Quartz oscillators or ceramic oscillators are generally manufactured as follows:
First, a quartz chip or a ceramic chip (hereinafter referred to as xe2x80x9coscillator chipxe2x80x9d) is cut off from a crystal, fired or similarly treated, and is then polished to have an outline and thickness of predetermined dimensions. Following this, metal is evaporated on the oscillator chip, thereby forming an electrode. The oscillation frequency of the oscillator is finely adjusted by adjusting the evaporation level, and then it is completed by being housed in a predetermined package.
If there is a crack, chip, flaw, or the like on an oscillator chip that has not yet had metal evaporated thereon, there is a possibility that the crystal impedance may vary abnormally, or the frequency may fluctuate, when changing the electrical power applied to the completed oscillator.
Also, if the evaporation level is increased when performing metal evaporation in order to perform wide frequency adjustment, the evaporation time will be increased, resulting lower productivity. Moreover, there is a possibility of the crystal impedance rising abnormally, and there is a risk of deterioration over time due to peeling of the evaporated metal.
Thus, oscillators are examined by visual observation or optical examination methods in order to detect cracks, chips, flaws, or the like on the oscillator chips.
Also, it is a widespread practice that oscillator chips that have not yet had metal evaporated thereon are inserted between parallel opposing electrodes, i.e. a plurality of electrodes that are arranged opposite each other, and a Cl meter, a network analyzer, etc. is connected to the oppositely arranged electrodes with parallel flat plates, and then the oscillation characteristics (oscillation frequency, crystal impedance, etc.) are measured to sort the oscillator chips.
As described above, it is necessary to perform an optical flaw detection examination and to measure electrically the oscillation characteristics in order to produce oscillators whose crystal impedance is low, which do not vary abnormally, and which have high frequency stability, even if the applied electrical power is changed.
In order to cope with such requirements, there are cases in which visual examination of oscillator chips is performed. However, since this is performed by people, the possibility that errors may occur must be considered, and hence visual examination alone will not lead to a complete solution of the problem.
Among inventions that have been proposed in order to solve this problem, Japanese Unexamined Patent Application Publication No. 2001-183310 entitled xe2x80x9cMethod For Examining Quartz Substrates and Device Thereofxe2x80x9d is known. This invention features a combination of an optical examination device and an electrical examination device, which enables both the aforementioned optical examination and electrical examination to be performed by a single unit. However, much trial and error is necessary to adjust the illumination and the optical system and to set the threshold of an image processing device in order to adjust the optical system or the image processing device so as to allow simple contaminations, which have no effect on characteristics, to be distinguished from flaws or chips. Moreover, there is a fine difference in setting depending on the equipment, and thus it is not easy to use the device perfectly. In addition, because the optical examination device includes cameras, optical systems, and image processing devices, which are expensive, it is not economical to provide these devices on all manufacturing lines.
The present invention contributes to solving the foregoing problem, and the object of the invention is to provide a method for testing characteristics of oscillators only by electrical examination without using optical systems and image processing devices, which are expensive and complex to set, in order to obtain oscillators whose crystal impedance will not increase abnormally, nor whose frequency will vary, even if the electrical power applied to the oscillators changes.
In order to achieve the above objects, a method for testing characteristics of oscillators according to the present invention comprises a signal source designed for variable frequency and output amplitude; an electrode for applying an output signal of the signal source to an oscillator; measurement means for measuring an electrical current that flows through the oscillator via the electrode, or a level of the signal passing through the oscillator; and memory means for storing the results from the measurement means, wherein signals with the same frequencies but different output amplitudes are applied a plurality of times from the signal source to the oscillator, and after the corresponding outputs of the measurement means have been stored in the memory means, it is determined whether the oscillator is conforming or nonconforming by comparing the outputs of the measurement means at the same frequencies for different output amplitudes.
In the method for testing characteristics of oscillators according to the present invention, a network analyzer comprises the signal source or the measurement means.